Oligomer preparation method and oligomer preparation device

ABSTRACT

Provided are a method for preparing an oligomer and an apparatus for preparing the same. The method for preparing an oligomer including: supplying a feed stream including a monomer to a reactor to perform an oligomerization reaction; supplying a first discharge stream from the reactor to a first separation device and supplying a second discharge stream from the reactor to a second separation device; recovering the monomer as an upper discharge stream from the second separation device and supplying a lower discharge stream from the second separation device to a third separation device; and supplying an upper discharge stream from the third separation device to the second separation device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Phase entry pursuant to 35 U.S.C.§ 371 of International Application No. PCT/KR2020/010466, filed on Aug.7, 2020, and claims the benefit of and priority to Korean PatentApplication No. 10-2019-0102511, filed on Aug. 21, 2019 and KoreanPatent Application No. 10-2020-0094665, filed on Jul. 29, 2020, theentire contents of which are incorporated by reference in their entiretyfor all purposes as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to a method for preparing an oligomer andan apparatus for preparing an oligomer, and more particularly, to amethod for preparing an oligomer and an apparatus for preparing anoligomer which efficiently recycle a monomer recovered in an oligomerproduction process.

BACKGROUND ART

An alpha-olefin is an important material which is used in comonomers,cleaning agents, lubricants, plasticizers, and the like and iscommercially widely used, and in particular, 1-hexene and 1-octene areoften used as the comonomer for adjusting the density of polyethylene inthe production of linear low-density polyethylene (LLDPE).

The alpha-olefins such as 1-hexene and 1-octene are producedrepresentatively by an oligomerization reaction of ethylene. Theethylene oligomerization reaction is performed by an oligomerizationreaction (trimerization reaction or tetramerization reaction) ofethylene using ethylene as a reactant, and the product produced by thereaction includes unreacted ethylene as well as a multi-componenthydrocarbon mixture including the desired 1-hexene and 1-octene. Theproduct is subjected to a separation process by a distillation column,in which the unreacted ethylene is recovered and reused in theoligomerization reaction of ethylene.

In recovering unreacted ethylene, in order to decrease an amount of aproduct or a by-product such as a solvent in a unreacted ethylene streamto be recovered, a separation device such as a distillation column or aflash drum is used. Here, since there is a great difference in boilingpoints between the unreacted ethylene and the product, a differencebetween an upper portion temperature and a lower portion temperature ofthe separation device increases. The upper portion and lower portiontemperatures of the separation device are determined by a pressure ofthe separation device, and when the pressure of the separation device ishigh, the upper portion and lower portion temperatures are raised, andwhen the pressure of the separation device is low, the upper portion andlower portion temperatures are lowered. In the case in which thepressure of the separation device is increased, when the pressure of theseparation device is increased, an upper portion temperature of theseparation device is raised so that it is easy to recover unreactedethylene, but a lower portion temperature of the separation device isalso raised so that decomposition and reaction of hydrocarbons such as aproduct and a solvent may be promoted, thereby lowering a productionyield of the product. However, in the case in which the pressure of theseparation device is decreased, a side reaction of hydrocarbons may besuppressed, but the upper portion temperature of the separation deviceis lowered, and thus, additional configurations such as using arefrigerant at a low temperature when recovering unreacted ethylene orinstalling a compressor having a high compression ratio are required,and in this case, process costs may be increased.

As such, a conventional method of recovering unreacted ethylene to reuseit in the oligomerization reaction has problems of having highinvestment costs and being economically infeasible, for example, havinga decreased production yield of the product, using a refrigerant at avery low temperature, installing a compressor having a high compressionratio, or the like.

DISCLOSURE Technical Problem

In order to solve the problems described in the Background Art, anobject of the present invention is to provide a method for preparing anoligomer and an apparatus for preparing an oligomer having reducedinvestment costs.

That is, an object of the present invention is to provide a method forpreparing an oligomer and an apparatus for preparing an oligomer inwhich in an oligomer production process, in recovering unreactedethylene to reuse it in an oligomerization reaction, investment costsare reduced, economic feasibility is improved, and a decrease in aproduction yield can be prevented since there is no need to use arefrigerant at a very low temperature or install a compressor having ahigh compression ratio.

Technical Solution

In one general aspect, a method for preparing an oligomer includes:supplying a feed stream including a monomer to a reactor to perform anoligomerization reaction; supplying a first discharge stream from thereactor to a first separation device and supplying a second dischargestream from the reactor to a second separation device; recovering themonomer as an upper discharge stream from the second separation deviceand supplying a lower discharge stream from the second separation deviceto a third separation device; and supplying an upper discharge streamfrom the third separation device to the second separation device.

In another general aspect, an apparatus for preparing an oligomerincludes: a reactor for oligomerizing a feed stream including a suppliedmonomer, supplying a first discharge stream to a first separationdevice, and supplying a second discharge stream to a second separationdevice; a first separation device for being supplied with the firstdischarge stream from the reactor; a second separation device for beingsupplied with the second discharge stream from the reactor to recoverthe monomer as an upper discharge stream and to supply a lower dischargestream to a third separation device; and a third separation device forbeing supplied with the lower discharge stream from the secondseparation device to supply an upper discharge stream to the secondseparation device.

Advantageous Effects

According to the method for preparing an oligomer and the apparatus forpreparing an oligomer of the present invention, in recovering theunreacted monomer, the second separation device is operated at a highpressure, the third separation device to which the lower dischargestream from the second separation device is connected is operated at alow pressure, the upper discharge stream from the third separationdevice is supplied to the second separation device to connect the secondseparation device and the third separation device, thereby concentratinga by-product having a boiling point higher than the monomer and lowerthan the oligomer product in a lower flow of the second separationdevice. Therefore, the second separation device is operated at a highpressure to lower the lower portion temperature while maintaining theupper portion temperature high, thereby suppressing the side reaction ofhydrocarbons while efficiently recovering the monomer.

In addition, the by-product concentrated from a circulated flow of thesecond separation device and the third separation device can be removedto decrease a loss of the monomer.

DESCRIPTION OF DRAWINGS

FIG. 1 is a process flowchart of a method for preparing an oligomeraccording to an exemplary embodiment of the present invention.

FIGS. 2 and 3 are process flowcharts of a method for preparing anoligomer according to the Comparative Examples, respectively.

DETAILED DESCRIPTION

The terms and words used in the description and claims of the presentinvention are not to be construed limitedly as having general ordictionary meanings but are to be construed as having meanings andconcepts meeting the technical ideas of the present invention, based ona principle that the inventors are able to appropriately define theconcepts of terms in order to describe their own inventions in the bestmode.

In the present invention, the term “stream” may refer to a fluid flow ina process, or may refer to a fluid itself flowing in a pipe.Specifically, the “stream” may refer to both a fluid itself flowing in apipe connecting each apparatus and a fluid flow. In addition, the fluidmay refer to a gas or a liquid.

Hereinafter, the present invention will be described in more detail forbetter understanding the present invention.

According to the present invention, a method for preparing an oligomeris provided. As the method for preparing an oligomer, a method forpreparing an oligomer including: supplying a feed stream including amonomer to a reactor to perform an oligomerization reaction; supplying afirst discharge stream from the reactor to a first separation device andsupplying a second discharge stream from the reactor to a secondseparation device; recovering the monomer as an upper discharge streamfrom the second separation device and supplying a lower discharge streamfrom the second separation device to a third separation device; andsupplying an upper discharge stream from the third separation device tothe second separation device, can be provided.

According to an exemplary embodiment of the present invention, in a stepof supplying a feed stream including a monomer to a reactor to performan oligomerization reaction, the feed stream including the monomer canbe supplied to the reactor, and the oligomerization reaction of themonomer can be performed in a liquid phase in a lower portion of thereactor. The oligomerization reaction may refer to a reaction in which amonomer is oligomerized. The oligomerization may be referred to astrimerization or tetramerization depending on the number of monomers tobe polymerized, and these are collectively called multimerization.

According to an exemplary embodiment of the present invention, themonomer can be ethylene and the oligomer can be an alpha-olefin. Thealpha-olefin is an important material which is used in comonomers,cleaning agents, lubricants, plasticizers, and the like and iscommercially widely used, and in particular, 1-hexene and 1-octene areoften used as a comonomer for adjusting the density of polyethylene inthe production of linear low-density polyethylene (LLDPE). Thealpha-olefin such as 1-hexene and 1-octene can be produced by, forexample, a trimerization reaction or tetramerization reaction ofethylene.

According to an exemplary embodiment of the present invention, the stepof performing the oligomerization reaction of the monomer can beperformed in a reactor appropriate for a continuous process, andpreferably performed under a reaction system including one or morereactors selected from the group consisting of a continuous stirred tankreactor (CSTR) and a plug flow reactor (PFR).

According to an exemplary embodiment of the present invention, theoligomerization reaction of the monomer can be performed by ahomogeneous liquid phase reaction, a slurry reaction having a catalystsystem in a partially or entirely not dissolved form, a two-phaseliquid/liquid reaction, or a bulk phase reaction or gas phase reactionin which the product acts as a main medium, in the presence or absenceof a solvent, by applying the reaction system and a common contacttechnology. Preferably, the step of performing the oligomerizationreaction of the monomer can be performed in the homogeneous liquid phasereaction.

According to an exemplary embodiment of the present invention, the stepof performing the oligomerization reaction can be performed at atemperature of 10° C. to 180° C., 30° C. to 150° C., or 50° C. to 120°C. In addition, the step of performing the oligomerization reaction canbe performed under a pressure of 15 bar to 100 bar, 20 bar to 80 bar, or25 bar to 60 bar. When ethylene is oligomerized within the temperaturerange and the pressure range, a selectivity to a desired alpha-olefincan be excellent, a by-product amount can be decreased, the operationalefficiency of a continuous process can be increased, and the costs canbe reduced.

According to an exemplary embodiment of the present invention, the feedstream including the monomer can include a gaseous monomer and asolvent.

The gaseous monomer included in the feed stream can be supplied as, forexample, a feed stream including an ethylene monomer separated from anaphtha cracking center (NCC) process as it is or after being subjectedto a storage step. In addition, the gaseous monomer can include a streamrecovered in the oligomer production process.

The solvent included in the feed stream can be supplied to the reactoras the feed stream. In some cases, as the solvent, a solvent recoveredafter being used in an oligomerization process can be reused.

According to an exemplary embodiment, in a step of supplying a firstdischarge stream from the reactor to a first separation device andsupplying a second discharge stream from the reactor to a secondseparation device, a common distillation column can be used as theseparation device.

According to the exemplary embodiment of the present invention, thefirst discharge stream can be a stream including the gaseous monomer.The first separation device can supply the upper discharge streamincluding the gaseous monomer to the reactor and supply the lowerdischarge stream including the liquid monomer to the second separationdevice. Here, the upper discharge stream from the first separationdevice can be mixed with the gaseous monomer stream which is separatelysupplied to the reactor in a mixer and supplied to the reactor, or canbe separately supplied to the reactor.

According to an exemplary embodiment of the present invention, thesecond discharge stream from the reactor can be supplied to the secondseparation device and be separated into the upper discharge streamincluding the gaseous monomer and the lower discharge stream includingan oligomer product, a by-product, and the solvent.

The gaseous monomer recovered from the second separation device as theupper discharge stream can be supplied to the reactor. Here, the upperdischarge stream from the second separation device can be mixed with thegaseous monomer stream which is separately supplied to the reactor andthe upper discharge stream from the first separation device in a mixerand supplied to the reactor, or can be separately supplied to thereactor.

The lower discharge stream from the second separation device can besupplied to the third separation device, and be separated into a liquidlower discharge stream including the oligomer and the solvent and aliquid upper discharge stream including a C4 compound as a by-product,in the third separation device. Here, the C4 compound can include1-butene (1-C4).

A content of the C4 compound included in the upper discharge stream fromthe third separation device can be 70 wt % or more. For example, thecontent of the C4 compound included in the upper discharge stream fromthe third separation device can be in a range of 70 wt % to 99 wt %, 80wt % to 95 wt %, or 85 wt % to 90 wt %. As such, as the upper dischargestream from the third separation device including the C4 compound issupplied to the second discharge stream, the second separation deviceand the third separation device can have a circulation flow. Here, theC4 compound is supplied from the third separation device as the upperdischarge stream to the second separation device, thereby concentratingthe C4 compound having a lower boiling point than the oligomer productand the solvent in a lower portion of the second separation device.Thus, as the unreacted monomer is recovered in an upper portion of thesecond separation device, a lower portion temperature is lowered and theC4 compound concentrated as the lower discharge stream can beeffectively removed.

The content of the C4 compound concentrated in the lower dischargestream from the second separation device can be 5 wt % to 40 wt %. Forexample, the content of the C4 compound included in the lower dischargestream from the second separation device can be in a range of 5 wt % to40 wt %, 10 wt % to 30 wt %, or 13 wt % to 20 wt %.

The lower discharge stream from the second separation device includingthe concentrated C4 compound is supplied to the third separation device,and the upper discharge stream including 80 wt % or more of the C4compound is discharged from the third separation device. Here, the C4compound can be efficiently separated in a manner of furcating andrecovering a part of the upper discharge stream from the thirdseparation device without supplying it to the second separation device.For example, the upper discharge stream from the third separation deviceincluding the C4 compound at a high content can be partially purged toselectively recover the C4 compound.

The content of the C4 compound included in the part of the upperdischarge stream from the third separation device can be 70 wt % ormore. For example, the content of the C4 compound included in the partof the upper discharge stream from the third separation device can be ina range of 70 wt % to 99 wt %, 80 wt % to 95 wt %, or 85 wt % to 90 wt%. In addition, a content of the monomer included in the part of theupper discharge stream from the third separation device can be 5 wt % orless. For example, the content of the monomer included in the part ofthe upper discharge stream from the third separation device can be in arange of 0.01 wt % to 5 wt %, 0.1 wt % to 3 wt %, or 0.5 wt % to 2 wt %.As such, in the method for preparing an oligomer according to thepresent invention, the part of the upper discharge stream from the thirdseparation device is purged while a loss of the monomer is minimized to5 wt % or less, thereby selectively recovering the C4 compound which isthe by-product in the process. Thus, a problem that in the conventionalmethod for preparing an oligomer, due to a low selectivity to the C4compound, when the C4 compound is removed by a method of purging a partof a unreacted monomer recover stream without a separate C4 separationstep, the monomer is also removed with the C4 compound, resulting in abig loss of the monomer, has been solved.

A ratio of the content of the C4 compound included in the upperdischarge stream from the third separation device to the content of theC4 compound included in the second discharge stream from the reactor canbe 2 or more, 2 to 7, or 4 to 6. Here, the upper discharge stream fromthe third separation device can mean a stream which is discharged froman upper portion of the third separation device and supplied to thesecond separation device. A ratio of the content of the C4 compoundincluded in the second discharge stream from the reactor to the contentof the C4 compound included in the upper discharge stream from the thirdseparation device can mean a concentration ratio of the concentrated C4compound in the second discharge stream from the reactor while thesecond discharge stream from the reactor is supplied to the secondseparation device, passes through the third separation device, and ispartially circulated. Specifically, the third separation device isinstalled at a rear end of the second separation device and the C4compound is concentrated at a concentration ratio of 2 times or more thecontent of the C4 compound in the second discharge stream from thereactor, thereby obtaining an effect of lowering a boiling point of thelower discharge stream from the second separation device due to a lowboiling point of the C4 compound, and thus, the lower portiontemperature of the second separation device can be lowered whilemaintaining the pressure of the second separation device high.Specifically, when a material having a low boiling point has anincreased concentration at the same pressure, an effect of lowering theboiling point of the mixture is shown, and thus, the boiling point ofthe lower discharge stream from the second separation device can belowered by concentrating the C4 compound. Here, since a boiling point ofthe stream discharged from the distillation column can mean an operationtemperature of the corresponding distillation column, the boiling pointof the lower discharge stream from the second discharge stream can meanan operation temperature of the lower portion of the second separationdevice.

According to an exemplary embodiment of the present invention, thepressure in the second separation device can be operated at higherpressure than the pressure in the third separation device. Specifically,the lower discharge stream including the monomer is discharged to thethird separation device while operating the second separation device ata high pressure, thereby lowering the lower portion temperature whilemaintaining the upper portion temperature of the second separationdevice high. Thus, the side reaction of hydrocarbons can be suppressed.Specifically, the upper portion temperature is maintained high and thelower portion temperature is lowered while operating the pressure of thesecond separation device high, thereby easily recovering the unreactedmonomer in the upper portion and preventing occurrence of a sidereaction in which the oligomer produced in the lower portion isdecomposed or reacted with other materials to produce a by-product.

The pressure in the second separation device can be in a range of 12 barto 25 bar, and the pressure in the third separation device can be in arange of 3 bar to 15 bar. For example, the pressure in the secondseparation device can be in a range of 12 bar to 25 bar, 13 bar to 23bar, or 14 bar to 20 bar, and the pressure in the third separationdevice can be in a range of 3 bar to 15 bar, 4 bar to 13 bar, or 5 barto 10 bar. The pressure in the second separation device or the thirdseparation device is controlled to the range described above, therebyefficiently recovering the unreacted monomer without requiring arefrigerant at a low temperature or a compressor having a highcompression ratio in the second separation device and the thirdseparation device, and preventing occurrence of a side reaction in whichthe oligomer produced by the oligomerization reaction of the monomer inthe lower portion of the second separation device is decomposed orreacted with other materials to produce a by-product.

The second separation device is operated at a high pressure, the lowerdischarge stream from the second separation device is supplied to thethird separation device operated at a low pressure, and the C4 compoundis concentrated in the lower portion of the second separation devicefrom the circulation flow between the second separation device at a highpressure and the third separation device at a low pressure, therebylowering the lower portion temperature while maintaining the upperportion temperature of the second separation device high. Specifically,the temperature of the lower discharge stream from the second separationdevice can be 130° C. to 200° C. For example, the temperature of thelower discharge stream from the second separation device can be 130° C.to 200° C., 140° C. to 190° C., or 150° C. to 180° C.

According to an exemplary embodiment of the present invention, in thelower discharge stream from the third separation device, the solvent andthe oligomer can be separated by an additional separation process, andthe separated solvent can be supplied to the reactor. In addition, theseparated oligomer can be separated again into a trimer, a tetramer, andthe like of the monomer by an additional separation process.

According to the present invention, an apparatus for preparing anoligomer is provided. As the apparatus for preparing an oligomer, anapparatus for preparing an oligomer including: a reactor foroligomerizing a feed stream including a supplied monomer, supplying afirst discharge stream to a first separation device, and supplying asecond discharge stream to a second separation device; a firstseparation device for being supplied with the first discharge streamfrom the reactor; a second separation device for being supplied with thesecond discharge stream from the reactor to recover the monomer as anupper discharge stream and to supply a lower discharge stream to a thirdseparation device; and a third separation device for being supplied withthe lower discharge stream from the second separation device to supplyan upper discharge stream to the second separation device, can beprovided.

According to an exemplary embodiment of the present invention, theapparatus for preparing an oligomer according to the present inventioncan be an apparatus for performing the process according to the methodfor preparing an oligomer described above.

According to an exemplary embodiment of the present invention, theapparatus for preparing an oligomer according to the present inventioncan be described with reference to the following FIG. 1. For example,the apparatus for preparing an oligomer includes a reactor 100 foroligomerizing a feed stream including a supplied monomer, and in thereactor 100, a first discharge stream including a gaseous monomer can besupplied to a first separation device 200 and a second discharge streamincluding a liquid monomer can be supplied to a second separation device210.

According to an exemplary embodiment of the present invention, the feedstream supplied to the reactor 100 can include the monomer and thesolvent. Specifically, the feed stream can include the gaseous monomerand the solvent. The feed stream including the gaseous monomer caninclude a gaseous monomer stream directly supplied to the reactor 100,the gaseous monomer recovered as the upper discharge stream from thefirst separation device 200, and the gaseous monomer recovered as theupper discharge stream from the second separation device 210. Thegaseous monomer stream directly supplied to the reactor 100, the upperdischarge stream from the first separation device 200 including thegaseous monomer, and the upper discharge stream from the secondseparation device 210 including the gaseous monomer can be separatelysupplied to the reactor 100, or supplied to the reactor 100 as a mixeddischarge stream mixed in a mixer (not shown). The solvent can beseparately supplied to the reactor 100, in which a solvent separatedafter being used in the process can be reused as the solvent.

According to an exemplary embodiment of the present invention, the firstseparation device 200 can be supplied with the first discharge streamfrom the reactor 100 and separated into the upper discharge streamincluding the gaseous monomer and the lower discharge stream includingthe liquid monomer. Here, the upper discharge stream from the firstseparation device 200 can be supplied to the reactor 100, and the lowerdischarge stream from the first separation device 200 can be supplied tothe second separation device 210.

According to an exemplary embodiment of the present invention, thesecond separation device 210 can be supplied with the second dischargestream from the reactor 100 and the lower discharge stream from thefirst separation device 200 including the liquid monomer, and can beseparated into the upper discharge stream including the gaseous monomerand the lower discharge stream including the oligomer product, theby-product, and the solvent. Here, the upper discharge stream from thesecond separation device 210 can be supplied to the reactor 100, and thelower discharge stream from the second separation device 210 can besupplied to the third separation device 220.

The upper discharge stream from the second separation device 210 canpass through a compressor 300 and be supplied to the reactor 100. Here,since the separation device 210 is operated at a high pressure of 12 barto 20 bar, the apparatus is economical in that the compressor 300 havinga relatively low compression ratio can be used. Therefore, process costscan be reduced as compared with the case of using the conventionalcompressor 300 having a high compression ratio.

The lower discharge stream from the second separation device 210 issupplied to the third separation device 220, and the upper dischargestream including the by-product including a C4 compound can be suppliedto the second separation device 210. Here, the upper discharge streamfrom the third separation device 220 can be supplied to the secondseparation device 210 using a pump 400. Specifically, the upperdischarge stream from the third separation device 220 is supplied to thesecond separation device 210 using the pump 400, and in this process,the pressure of the upper discharge stream from the third separationdevice 220 can be increased to the pressure of the second separationdevice 210.

A part of the upper discharge stream from the third separation device220 is not supplied to the second separation device 210 but recovered.Specifically, the upper discharge stream from the third separationdevice 220 can be purged to recover a part of the stream including theC4 compound and the remaining stream can be supplied to the secondseparation device 210.

The lower discharge stream including the oligomer product and thesolvent can be recovered from the third separation device 220. Here, theoligomer product and the solvent included in the lower discharge streamfrom the third separation device 220 can be separated by an additionalseparation device (not shown), and the separated solvent can be reusedin the oligomer production process. In addition, example, in the case inwhich the oligomerization reaction is performed using an ethylenemonomer as the monomer, the oligomer product can include 1-hexene and1-octene. In this case, 1-hexene and 1-octene can be separated by anadditional separation device (not shown) or separated by a separateprocess and used.

According to an exemplary embodiment of the present invention, in somecases, a condenser (not shown) can be further installed in an upperportion of any one or more of the first separation device 200, thesecond separation device 210, and the third separation device 220, and areboiler (not shown) can be further installed in a lower portionthereof.

Hereinabove, the method for preparing an oligomer and the apparatus forpreparing an oligomer according to the present invention have beendescribed and illustrated in the drawings, but the description and theillustration in the drawings are the description and the illustration ofonly core constitutions for understanding of the present invention, andin addition to the process and apparatus described above and illustratedin the drawings, the process and the apparatus which are not describedand illustrated separately may be appropriately applied and used forcarrying out the method for preparing an oligomer and the apparatus forpreparing an oligomer according to the present invention.

Hereinafter, the present invention will be described in more detail bythe Examples. However, the following Examples are provided forillustrating the present invention. It is apparent to a person skilledin the art that various modifications and alterations may be madewithout departing from the scope and spirit of the present invention,and the scope of the present invention is not limited thereto.

EXAMPLES Example 1

For the process flowchart illustrated in FIG. 1, the process wassimulated using an Aspen Plus simulator from Aspen Technology, Inc.Here, the lower discharge stream from the second separation device 210was a stream passing a reboiler (not shown), the upper discharge streamfrom the third separation device 220 was a stream passing a condenser(not shown), and the lower discharge stream from the third separationdevice 220 was a stream passing the reboiler (not shown). In addition,ethylene (C2) was supplied as the monomer at a reaction amount of 20,000kg/hr or more, the reaction conditions of the reactor 100 were set at atemperature of 53° C. and a pressure of 30 bar, the operation pressureof the second separation device 210 was set at 15 bar, and the operationpressure of the third separation device 220 was set at 6 bar. Theresults are shown in the following Table 1.

TABLE 1 Stream Stream Stream Stream Stream Stream Stream 1 2 3 4 5 6 7Temperature 53 45 160 41 43 41 161 (° C.) Pressure 30 15 15 6 15 6 6(bar) Flow rate kg/hr wt % kg/hr wt % kg/hr wt % kg/hr wt % kg/hr wt %kg/hr wt % kg/hr wt % Ethylene 6861 14 6859 77 88 0 88 1 86 1 2 1 0 01-C4 1750 4 1604 18 8194 17 8193 85 8048 85 145 85 1 0 1-C6 9269 19 2443 10279 21 1277 13 1254 13 23 13 9002 23 Solvent 20096 40 127 1 20022 4053 1 52 1 1 1 19969 50 Heavy 10894 23 24 1 10871 22 1 0 1 0 0 0 10870 27Total flow 48870 100 8858 100 49453 100 9611 100 9441 100 170 100 39842100 rate Heavy: a substance having a higher molecular weight than thesolvent Stream 1: the second discharge stream from the reactor 100 whichwas supplied from the reactor 100 to the second separation device 210Stream 2: the upper discharge stream from the second separation device210 Stream 3: the lower discharge stream from the second separationdevice 210 Stream 4: the upper discharge stream from the thirdseparation device 220 Stream 5: the upper discharge stream from thethird separation device 220 which was supplied from the third separationdevice 220 to the pump 400. Stream 6: the part of the upper dischargestream from the third separation device 220 which was not supplied tothe pump but recovered Stream 7: the lower discharge stream from thethird separation device 220

In the table of the present invention, the flow rates of the componentsin the stream were indicated by rounding off the numbers to the nearesttenth, and when the flow rate was indicated as wt %, it was calculatedas a content of a component flow rate in the total flow rate.

Referring to Table 1, a ratio of the 1-C4 content in the seconddischarge stream from the reactor 100, which was supplied to the secondseparation device 210, and the 1-C4 content in the stream circulatedthrough the second separation device 210 and the third separation device220 and then back to the second separation device 210, that is, aconcentration ratio of 1-C4 was about 4.6, and it was confirmedtherefrom that the 1-C4 content in the lower discharge stream from thesecond separation device 210 was 17 wt %. In addition, the 1-C4 contentin the stream separated by purging a part of the upper discharge streamfrom the third separation device 220 was 85 wt % and the content of theethylene monomer was 1 wt %, and it was found therefrom that a 1-C4purity was high and there was little loss of the ethylene monomer.

Example 2

The process was performed in the same manner as in Example 1, exceptthat the operation pressure of the second separation device 210 was setat 18 bar and the operation pressure of the third separation device 220was set at 8 bar. The results are shown in the following Table 2.

TABLE 2 Stream Stream Stream Stream Stream Stream Stream 1 2 3 4 5 6 7Temperature 53 47 160 43 45 43 176 (° C.) Pressure 30 18 18 8 18 8 8(bar) Flow rate kg/hr wt % kg/hr wt % kg/hr wt % kg/hr wt % kg/hr wt %kg/hr wt % kg/hr wt % Ethylene 6861 14 6857 77 286 1 286 2 282 2 4 2 0 01-C4 1750 4 1615 18 10023 19 10023 80 9888 80 135 80 0 0 1-C6 9269 19237 3 11188 21 2185 17 2156 17 29 17 9003 23 Solvent 20096 41 118 120053 38 76 1 75 1 1 1 19977 50 Heavy 10894 22 23 0 10872 21 1 0 1 0 0 010871 27 Total 48870 100 8850 99 52423 100 12572 100 12403 100 169 10039851 100 flow rate Heavy: a substance having a higher molecular weightthan the solvent Stream 1: the second discharge stream from the reactor100 which was supplied from the reactor 100 to the second separationdevice 210 Stream 2: the upper discharge stream from the secondseparation device 210 Stream 3: the lower discharge stream from thesecond separation device 210 Stream 4: the upper discharge stream fromthe third separation device 220 Stream 5: the upper discharge streamfrom the third separation device 220 which was supplied from the thirdseparation device 220 to the pump 400 Stream 6: the part of the upperdischarge stream from the third separation device 220 which was notsupplied to the pump but recovered Stream 7: the lower discharge streamfrom the third separation device 220

Referring to Table 2, when the operation pressure of the secondseparation device 210 was set at 18 bar and the operation pressure ofthe third separation device 220 was set at 8 bar, the 1-C4 content inthe stream separated by purging a part of the upper discharge streamfrom the third separation device 220 was 80 wt % and the content of theethylene monomer was 2 wt %, and it was found therefrom that a 1-C4purity was high and there was little loss of the ethylene monomer.

In addition, as compared with Example 1, the pressure of the secondseparation device 210 was high, but the concentration flow and theconcentration ratio of 1-C4 was increased by increasing Stream 5,whereby the temperature of the lower discharge stream from the secondseparation device 210 was operated at 160° C. in the same manner as inExample 1.

Comparative Example Comparative Example 1

For the process flowchart illustrated in FIG. 2, the process wassimulated using an Aspen Plus simulator from Aspen Technology, Inc.Here, the upper discharge stream from the second separation device 210was a stream passing the condenser (not shown) and the lower dischargestream from the second separation device 210 was a stream passing thereboiler (not shown). In addition, ethylene (C2) was supplied as themonomer at a reaction amount of 20,000 kg/hr or more, the reactionconditions of the reactor 100 were set at a temperature of 53° C. and apressure of 30 bar, and the operation pressure of the second separationdevice 210 was set at 15 bar. The results are shown in the followingTable 3.

TABLE 3 Stream 1-1 Stream 2-1 Stream 3-1 Temperature 53 7 212 (° C.)Pressure 30 15 15 (bar) Flow rate kg/hr wt % kg/hr wt % kg/hr wt %Ethylene 6861 14 46861 81 0 0 1-C4 1750 4 1600 19 150 0 1-C6 9269 19 0 09268 23 Solvent 20096 41 0 0 20096 50 Heavy 10894 22 0 0 10894 27 Totalflow 48870 100 8461 100 40409 100 rate Heavy: a substance having ahigher molecular weight than the solvent Stream 1-1: the seconddischarge stream from the reactor 100 which was supplied from thereactor 100 to the second separation device 210 Stream 2-1: the upperdischarge stream from the second separation device 210 Stream 3-1: thelower discharge stream from the second separation device 210

Referring to Table 3, though in Comparative Example 1, the secondseparation device 210 was operated at 15 bar in the same manner as inExample 1, the temperature of Stream 3-1 which was the lower dischargestream from the second separation device 210 was 212° C., which wasfound to be significantly higher than 160° C. of Example 1. In addition,in Example 2 in which the operation pressure of the second separationdevice 210 was higher than 15 bar also, the temperature of the lowerdischarge stream from the second separation device 210 was 160° C.,which was found to be significantly lower than the temperature ofComparative Example 1.

In addition, as compared with Examples 1 and 2 in which the content 1-C4content in the lower discharge stream from the second separation device210 was 17 wt % and 19 wt %, respectively, it was confirmed in theComparative Example that the 1-C4 content in the lower discharge streamfrom the separation device 210 was less than 0.5 wt %.

As a result, the reason why the temperature of the lower dischargestream from the second separation device 210 in Comparative Example 1was high in spite of operating the apparatus at the same or lowerpressure is considered as being that the third separation device 220connected to the lower discharge stream from the second separationdevice 210 was absent and 1-C4 was not concentrated in the lower portionof the second separation device 210 due to the absence of the thirdseparation device 220.

Comparative Example 2

The same process was performed in the same manner as in ComparativeExample 1, except that the operation pressure of the second separationdevice 210 was set at 6 bar for lowering the lower portion temperatureof the second separation device 210 to 160° C. as in Example 1. Theresults are shown in the following Table 4.

TABLE 4 Stream 1-1 Stream 2-1 Stream 3-1 Temperature 53 −16 160 (° C.)Pressure 30 6 6 (bar) Flow rate kg/hr wt % kg/hr wt % kg/hr wt %Ethylene 6861 14 46861 81 0 0 1-C4 1750 4 1600 19 150 0 1-C6 9269 19 0 09269 23 Solvent 20096 41 0 0 20096 50 Heavy 10894 22 0 0 10894 27 Totalflow 48870 100 8461 100 40409 100 rate Heavy: a substance having ahigher molecular weight than the solvent Stream 1-1: the seconddischarge stream from the reactor 100 which was supplied from thereactor 100 to the second separation device 210 Stream 2-1: the upperdischarge stream from the second separation device 210 Stream 3-1: thelower discharge stream from the second separation device 210

Referring to Table 4, in Comparative Example 2, the temperature ofStream 3-1 which was the lower discharge stream from the secondseparation device 210 was lowered to 160° C. as in Example 1, byoperating the second separation device 210 at 6 bar; however, in thiscase, since the pressure of the upper discharge stream from the secondseparation device 210 which was discharged at 6 bar was increased byabout 24 bar for supplying the upper discharge stream to the reactor, itwas confirmed that two compressors 300 having a compression ratio of upto 3 times should be generally used as shown in FIG. 3. In addition,since only the pressure of the second separation device 210 was loweredwhile maintaining the composition of the stream supplied to the secondseparation device 210, as compared with Example 1, the temperature ofStream 2-1 was also lowered like the lowered temperature of Stream 3-1to become −16° C. As such, since a refrigerant having a lowertemperature level than a refrigerant such as a coolant and an ethyleneglycol antifreeze which are generally used in the process should be usedfor cooling the upper discharge stream from the second separation device210 to −16° C., there is a problem of separate investment costs andoperating costs.

The invention claimed is:
 1. A method for preparing an oligomer, themethod comprising: supplying a feed stream including a monomer to areactor to perform an oligomerization reaction; supplying a firstdischarge stream from the reactor to a first separation device andsupplying a second discharge stream from the reactor to a secondseparation device; recovering the monomer as an upper discharge streamfrom the second separation device and supplying a lower discharge streamfrom the second separation device to a third separation device; andsupplying an upper discharge stream from the third separation device tothe second separation device.
 2. The method for preparing an oligomer ofclaim 1, wherein the upper discharge stream from the third separationdevice is a liquid stream including a C4 compound.
 3. The method forpreparing an oligomer of claim 2, wherein a part of the upper dischargestream from the third separation device is not supplied to the secondseparation device but recovered.
 4. The method for preparing an oligomerof claim 3, wherein a content of the C4 compound included in the part ofthe upper discharge stream from the third separation device is 70 wt %or more.
 5. The method for preparing an oligomer of claim 3, wherein acontent of the monomer included in the part of the upper dischargestream from the third separation device is 5 wt % or less.
 6. The methodfor preparing an oligomer of claim 1, wherein the lower discharge streamfrom the second separation device comprises a C4 compound in an amountof 5 wt % to 40 wt %.
 7. The method for preparing an oligomer of claim1, wherein the upper discharge stream from the third separation deviceand the second discharge stream from the reactor include a C4 compound,and wherein a ratio of the content of the C4 compound included in theupper discharge stream from the third separation device to the contentof the C4 compound included in the second discharge stream from thereactor is 2 or more.
 8. The method for preparing an oligomer of claim1, wherein the second separation device is operated at a higher pressurethan the third separation device.
 9. The method for preparing anoligomer of claim 8, wherein the pressure in the second separationdevice is 12 bar to 25 bar and the pressure in the third separationdevice is 3 bar to 15 bar.
 10. The method for preparing an oligomer ofclaim 1, wherein a temperature of the lower discharge stream from thesecond separation device is 130° C. to 200° C.
 11. The method forpreparing an oligomer of claim 1, wherein the monomer is ethylene andthe oligomer is an alpha-olefin.
 12. An apparatus for preparing anoligomer comprising: a reactor for oligomerizing a feed stream includinga monomer, supplying a first discharge stream to a first separationdevice, and supplying a second discharge stream to a second separationdevice; the first separation device for being supplied with the firstdischarge stream from the reactor; the second separation device forbeing supplied with the second discharge stream from the reactor torecover the monomer as an upper discharge stream and to supply a lowerdischarge stream to a third separation device; and the third separationdevice for being supplied with the lower discharge stream from thesecond separation device to supply an upper discharge stream to thesecond separation device.